A high sensitive fluorescence turn-on probe for imaging Zn2+ in aqueous solution and living cells

A new pyrazoline-based fluorescent probe was designed and synthesized. The probe can induce a 60-fold fluorescence enhancement after 5 equiv. of Zn2+ was added, which is superior to a previous report (13-fold), and exhibits high sensitivity and selectivity for response to Zn2+ in aqueous solution. The detection limit and association constant were calculated as 1.23 × 10−7 M and 3.89 × 103 M−1 by a fluorescence titration experiment. The 1 : 1 binding stoichiometry of L–Zn2+ complex was analysed by Job's plot. The probe showed good reversibility upon addition of EDTA or TPEN. Furthermore, the probe L showed good membrane permeability and can be applied to monitor Zn2+ ions in living HeLa cells.